It is well known that the self-cleaning processes which take place in watercourses, thanks to the mobility of their waters, and when the organic loads present in them do not exceed given limits, also take place in water basins, but at insufficient levels and with poor or no results.
In particular, natural or artificial water basins, lakes or ponds, owing to the insufficent mobility of their waters, are not able to eliminate some so-called nutrient substances, i.e. substances which contribute to the development of forms of animal or vegetal life; such substances mainly consist of phosphorus and nitrogen compounds (phosphates and nitrates).
Since water retaining times in said water basins are very long, the nutrient substances accumulate, particularly in zones of the basin where the water turnover is rather slow and difficult, bringing about so-called eutrophication phenomena.
In substance, in a basin rich of nutrient substances such chain reactions are started, which cause, in warm seasons, the development of large amounts of algae and other aquatic plants, favoured by the high concentration of nutrients while in cold seasons most of the grown aquatic flora dies and falls to the bottom of the basin.
The organic matter at the bottom of the basin decomposes, absorbing large amounts of oxygen and bringing about anaerobic conditions, i.e. lack of oxygen, which originate in the bottom but progressively spread to the surrounding aquatic environment.
As a consequence, the complex biological equilibrium existing in the basin is seriously upset, and in particular toxic substances are released and consequent fish mortality occurs.
In brief, the eutrophication process, generated by an excessive supply of nutrient substances, consists in an excessive production of algae which brings about an excessive consumption of oxygen and the consequent degradation of the basin environment.
Known systems of intervention provide for the artificial aeration of basin waters. For instance, the aeration by air diffused at the bottom of the basin, carried out by means of perforated pipes, makes it possible to achieve a continuous turnover of water at the bottom, which is, therefore, sufficiently oxygenated.
However, such a system is suited to be used only as an emergency step, since it does not tackle the problem at its roots, i.e. by eliminating the nutrient substances, but simply preventing anaerobic conditions from originating at the bottom. Once aeration is stopped, the eutrophication situation is quickly re-established. In other cases, surface aerators, e.g. floating aerators, are resorted to, which bring about a stirring up of waters so increasing their oxygenation. Such mechanical means, operating at the surface, basically consist of a motor, fastened onto a floating platform, which drags a turbine into rotation. A diffuser is designed to diffuse the water column raised by the turbine in the surrounding area, so to cause an increase of the amount of oxygen dissolved in water.
The aeration carried out in this way brings about the oxidation of a part of phosphorus components and their trasnformation into products having a high degree of oxidation (orthophosphates).
However, some additional treatments, mainly of chemical nature, are later required, since the transformation of phosphorus compounds into compounds having a high oxidation degree, which are immediately assimilable by plants and organisms in general, may make the situation of eutrophication worse, instead of improving it.
Moreover, the turbine blades swallow up, together with water, also fishes which find themselves near the aerator, causing their death, and this negatively affects the yield of any fish-breeding activity carried on in the basin.
From the FR 2.364.181 a device is known for bioaeration of water.
With this device the oxidation of phosphorus is obtained by pumping the water into a cylinder dipped into the basin to be purified.
The water is taken from the basin by means of a pipe connected to a pump and then conveyed to the cylinder.
In the section of pipe from the pump to the cylinder, there is a Venturi tube, that causes air to be sucked from the outside, by means of a smaller pipe, and to be mixed with the water sent to the cylinder.
The water and air swirl in the cylinder producing a froth that floats on the water surface and is conveyed away through a large diameter pipe.
This large diameter pipe closes, with a cone-shaped end, the open upper extremity of the cylinder.
Lastly, the water is discharged in the basin through an opening 6 made in the base fo the cylinder.